I. Field
The present invention relates generally to communication, and more specifically to techniques for multiplexing and transmitting multiple data streams in a wireless multi-carrier communication system.
II. Background
A multi-carrier communication system utilizes multiple carriers for data transmission. These multiple carriers may be provided by orthogonal frequency division multiplexing (OFDM), some other multi-carrier modulation techniques, or some other construct. OFDM effectively partitions the overall system bandwidth into multiple orthogonal subbands. These subbands are also referred to as tones, carriers, subcarriers, bins, and frequency channels. With OFDM, each subband is associated with a respective subcarrier that may be modulated with data.
A base station in a multi-carrier system may simultaneously transmit multiple data streams for broadcast, multicast, and/or unicast services. A data stream is a stream of data that may be of independent reception interest to a wireless device. A broadcast transmission is sent to all wireless devices within a designated coverage area, a multicast transmission is sent to a group of wireless devices, and a unicast transmission is sent to a specific wireless device. For example, a base station may broadcast a number of data streams for multimedia (e.g., television) programs via a terrestrial radio link for reception by wireless devices. This system may employ a conventional multiplexing and transmission scheme such as, for example, Digital Video Broadcasting-Terrestrial (DVB-T) or Integrated Services Digital Broadcasting-Terrestrial (ISDB-T). Such a scheme would first multiplex all of the data streams to be transmitted onto a single high-rate composite stream and then process (e.g., encode, modulate, and up-convert) the composite stream to generate a modulated signal for broadcast via the radio link.
A wireless device within the coverage area of the base station may be interested in receiving only one or few specific data streams among the multiple data streams carried by the composite stream. The wireless device would need to process (e.g., down-convert, demodulate, and decode) a received signal to obtain a high-rate decoded data stream and then demultiplex this stream to obtain the one or few specific data streams of interest. This type of processing may not be a problem for receiver units intended to be powered on all the time, such as those used in homes. However, many wireless devices are portable and powered by internal batteries. Continuous demodulation and decoding of the high-rate composite stream to recover just one or few data streams of interest consumes significant amounts of power. This can greatly shorten the “ON” time for the wireless devices, which is undesirable.
There is therefore a need in the art for techniques to transmit multiple data streams in a multi-carrier system such that they can be received by wireless devices, with minimal power consumption.